FinFET structures having silicon germanium and silicon fins

ABSTRACT

A finned structure is fabricated using a bulk silicon substrate having a carbon doped epitaxial silicon layer. A pFET region of the structure includes silicon germanium fins. Such fins are formed by annealing the structure to mix a germanium containing layer with an adjoining crystalline silicon layer. The structure further includes an nFET region including silicon fins formed from the crystalline silicon layer. The germanium containing layer in the nFET region is removed to create a space beneath the crystalline silicon layer in the nFET region. An insulating material is provided within the space. The pFET and nFET regions are electrically isolated by a shallow trench isolation region.

FIELD

The present disclosure relates to the physical sciences, and, moreparticularly, to fin-type field effect transistor (FinFET) structuresand methods of fabrication thereof.

BACKGROUND

Some types of field effect transistors (FETs) have three-dimensional,non-planar configurations including fin-like structures extending abovesubstrates. Such field effect transistors are referred to as FinFETs.The substrates may include semiconductor on insulator (SOI) substratesor bulk semiconductor substrates. Silicon fins are formed in someFinFETs on substrates via known technology such as sidewall imagetransfer (SIT). FinFET structures including SOI substrates can beformed, in part, by selectively etching the crystalline silicon layersdown to the oxide or other insulating layers thereof followingphotolithography. Active fin heights are set by SOI thickness whenemploying SOI substrates. In bulk FinFETs, active fin height is set byoxide thickness and etched fin height. The gates of FinFETs can beformed using a “gate-first” process wherein a gate stack and spacers areformed prior to selective epitaxial growth wherein source and drainregions are enlarged. A “gate-last” process may alternatively beemployed wherein the source/drain regions are formed immediatelyfollowing fin patterning. Gate-last procedures can involve making adummy gate, fabricating other elements of the transistor, removing thedummy gate, and replacing the removed dummy gate with actual gatematerials.

Doped semiconductor material may be provided by selective epitaxialgrowth on the sidewalls of the fin structure(s) during fabrication ofFinFETs. Such growth results in faceted structures that, in some cases,merge into a continuous volume.

SUMMARY

Principles of the present disclosure provide an exemplary fabricationmethod that includes obtaining a structure comprising a bulk siliconsubstrate, an epitaxial layer comprising carbon doped silicon on thesubstrate, an epitaxial layer containing germanium on the carbon dopedsilicon layer, and a layer comprising crystalline silicon on thegermanium containing layer. An isolation region is formed on thestructure, electrically isolating a first region of the structure from asecond region of the structure. The method further includes removing thegermanium containing layer from the second region of the structure,thereby forming a space within the second region beneath the crystallinesilicon layer, forming an insulating layer within the space, thermallymixing the germanium containing layer and the crystalline silicon layerin the first region of the structure to form a layer comprising silicongermanium, forming a plurality of fins comprising silicon germanium inthe first region from the silicon germanium layer, and forming aplurality of fins from the crystalline silicon layer in the secondregion.

A further exemplary fabrication method includes depositing an epitaxialcarbon doped silicon layer on an essentially undoped silicon substrate,depositing an epitaxial silicon germanium layer on the carbon dopedsilicon layer, and depositing an essentially undoped epitaxial siliconlayer on the silicon germanium layer, thereby forming a first structurecomprising the silicon substrate, the carbon doped silicon layer, thesilicon germanium layer and the epitaxial silicon layer. A shallowtrench isolation region is formed within the first structure. Thesilicon germanium layer on a first side of the shallow trench isolationregion is removed, thereby forming a space within the first structurebeneath the epitaxial silicon layer. The space is filled with anelectrically insulating material. The method further includes the stepof thermally mixing the silicon germanium layer and the epitaxialsilicon layer on a second side of the shallow trench isolation region,thereby forming a silicon germanium surface layer. A first set ofparallel fins is formed from the epitaxial silicon layer on the firstside of the shallow trench isolation region and a second set of parallelfins is formed from the silicon germanium surface layer on the secondside of the shallow trench isolation region.

A structure in accordance with an exemplary embodiment includes a bulksilicon substrate and an epitaxial carbon doped silicon layer on thebulk silicon substrate. The structure further includes a plurality offins comprising silicon germanium adjoining a first portion of theepitaxial carbon doped silicon layer. An insulating layer adjoins asecond portion of the epitaxial carbon doped silicon layer. A pluralityof fins comprising crystalline silicon adjoins the insulating layer. Anisolation region electrically isolates the first and second portions ofthe epitaxial carbon doped silicon layer.

As used herein, “facilitating” an action includes performing the action,making the action easier, helping to carry the action out, or causingthe action to be performed. Thus, by way of example and not limitation,instructions executing on one processor might facilitate an actioncarried out by instructions executing on a remote processor, by sendingappropriate data or commands to cause or aid the action to be performed.For the avoidance of doubt, where an actor facilitates an action byother than performing the action, the action is nevertheless performedby some entity or combination of entities.

FinFET structures and fabrication methods as disclosed herein canprovide substantial beneficial technical effects. For example, one ormore embodiments may provide one or more of the following advantages:

-   -   Enhanced FinFET performance;    -   Avoidance of defects in fin structures;    -   Different materials for nFET and pFET fins with uniform fin        height (topography);    -   Different channel materials for nFET and pFET devices so nFET        and pFET characteristics can be independently optimized.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a bulk silicon substrate;

FIG. 2 is a schematic illustration of the substrate of FIG. 1 includinga layer of carbon doped silicon formed thereon;

FIG. 3 is a schematic illustration of the structure of FIG. 2 showing asilicon germanium layer deposited on the carbon doped silicon layer;

FIG. 4 is a schematic illustration of the structure of FIG. 3 showing asilicon layer deposited epitaxially on the silicon germanium layer;

FIG. 5 is a schematic illustration showing formation of a shallow trenchisolation (STI) region on the substrate shown in FIG. 4;

FIG. 6 is a schematic illustration showing formation of a hard mask onthe epitaxial silicon layer of the structure of FIG. 5 and the formationof an opening within the hard mask;

FIG. 7 is a schematic illustration showing removal of a portion of thesilicon layer beneath the opening in the hard mask;

FIG. 8 is a schematic illustration showing removal of a portion of thesilicon germanium layer of the structure shown in FIG. 7;

FIG. 9 is a schematic illustration showing removal of the hard mask andfilling of the region between the epitaxial silicon and carbon dopedsilicon layers formerly containing silicon germanium;

FIG. 10 is a schematic illustration showing formation of a hard maskover a portion of the structure shown in FIG. 9;

FIG. 11 is a schematic illustration showing formation of a silicongermanium layer from adjoining layers of silicon and silicon germanium;

FIG. 12 shows the removal of the hard mask from the structure shown inFIG. 11 and formation of silicon and silicon germanium fins, and

FIG. 13 is a schematic illustration showing the structure of FIG. 12following deposition of an insulating material within channels formed bythe silicon germanium fins.

DETAILED DESCRIPTION

FinFET structures are characterized by fins formed on semiconductorsubstrates. Such substrates include bulk silicon substrates (fin onbulk) and SOI substrates (fin on

SOI) as discussed above. The processes discussed below are applicable tofabrication of FinFET structures from bulk substrates where sets of finscomprising silicon and silicon germanium are desired. FIGS. 1-12illustrate exemplary steps that may be performed sequentially infabricating a structure, it being appreciated that additional steps maybe necessary depending on the desired features of the structure.Fabrication may commence with a partially completed structure, in whichcase one or more of the steps described below could be omitted.

A bulk substrate 20 comprised of essentially undoped crystalline siliconis shown in FIG. 1, it being appreciated that standard siliconsubstrates may have a very low level of p-doping. The substrate may bein the form of a wafer. Referring to FIG. 2, a carbon doped silicon(Si:C) layer 22 is deposited epitaxially, for example via chemical vapordeposition (CVD), on the substrate 20. Carbon is electrically inactiveand prevents the diffusion of germanium into underlying layers. Thethickness of the Si:C layer is at least five nanometers (5 nm) in one ormore exemplary embodiments. The deposited material has an atomic carbonconcentration of between about 0.2-4% substitutional carbon in one ormore exemplary embodiments. In other embodiments, the layer 22 has aconcentration of about 0.3 to about 2.5% substitutional carbon. It isunderstood that the total amount of carbon in the carbon doped siliconlayer 22 may be higher than the substitutional amount.

Referring to FIG. 3, a germanium-containing layer 24, preferably silicongermanium is deposited epitaxially, for example by CVD, on the carbondoped silicon layer 22. In one or more embodiments, thegermanium-containing layer comprises 20-99% germanium, though morepreferably 20-80% germanium to minimize or avoid potential crystaldefects in the resulting structure. In other embodiments, the layercontains 30-60% germanium. The germanium content should be sufficientsuch that there is high selectivity between the germanium-containinglayer and silicon during an etching process to be described below. Thethickness of the germanium-containing layer in one or more embodimentsis between five to twenty-five nanometers (5-25 nm). As will beappreciated from the discussion below, the germanium-containing layershould have sufficient thickness and sufficient germanium content thatfins formed in the pFET region of the resulting structure contain anacceptable ratio of silicon and germanium for pFET applications.

As shown in FIG. 4, an essentially undoped epitaxial silicon layer 26 isformed on the germanium-containing layer 24 by CVD or other suitableprocess. The thickness of this layer corresponds to the fin heightdesired for the finished product and is chosen accordingly. In one ormore embodiments, the thickness of the epitaxial silicon layer 26 istwenty to thirty nanometers. The epitaxial silicon layer 26 does notcontain germanium and is accordingly well suited for nFET applications,as discussed further below.

A shallow trench isolation (STI) region 28 is formed in the structureshown in FIG. 4, resulting in the structure shown in FIG. 5. A trench isformed in the structure, for example by reactive ion etching, down tothe substrate 20. Patterning techniques familiar to those skilled in theart facilitate trench formation and subsequent filling of the trenchwith one or more electrically insulating material(s) such as silicondioxide. Shallow trench isolation (STI) provides a region 28 thatelectrically isolates active areas of the structure.

Referring to FIG. 6, a hard mask 30 is formed over the silicon layer 26and STI region 28. A nitride (silicon nitride (Si₃N₄)) hard mask isemployed in one or more embodiments. Such a mask may be deposited usingconventional deposition techniques such as spin-on coating, CVD,plasma-assisted CVD, or other known techniques. Conventional processesare further employed, such as applying and patterning a resist, etching,and removing resist, to remove a portion of the hard mask 30 from theregion of the structure to be used as an nFET region. A portion of thesilicon layer 26 is accordingly exposed in the nFET region of thestructure by a trench 32 formed in the hard mask 30. Hot phosphoric acidis an exemplary etchant that may be employed to form the trench 32 in anitride hard mask.

Referring to FIG. 7, the trench 32 is extended down to at least thegermanium containing layer 24 and possibly to the carbon doped siliconlayer 22. Reactive ion etching (RIE) through the opening in the hardmask 30 is employed in one or more exemplary embodiments to extend thetrench 32 so that access to the germanium containing layer 24 can beobtained for further processing.

Once access to the germanium containing layer 24 in the nFET region ofthe structure is obtained, the germanium containing layer 24 in thisregion is removed. Such removal creates a tunnel or space 34 between thesilicon layer 26 and the carbon doped silicon layer 22 in the nFETregion of the structure. A “silicon on nothing” (SON) region isaccordingly formed. Selective vapor phase etching using hydrogenchloride (HCl) at high temperature (for example 650-750° C.) is anexemplary technique to form the structure shown in FIG. 8 and can beconducted in the CVD tool employed in one or more of the steps describedabove. As discussed above, the germanium containing layer 24 shouldinclude sufficient germanium such that there is high selectivity betweenthis layer and silicon. A relatively high germanium content in the layer24 facilitates the etching process. In one exemplary embodiment, thegermanium containing layer 24 comprises sixty percent (60%) germanium.

Referring to FIG. 9, the hard mask 30 is removed from the structureusing hot phosphoric acid if the hard mask is a nitride mask, or othersuitable technique. The space 34 formed by removal of the germaniumcontaining layer 24 from the nFET region is filled with an oxidematerial 36 such as silicon dioxide. The filling process can be done bya deposition process (e.g., by CVD, spin-on, etc.) followed by an etchback process (e.g., wet etch, dry etch or combination of both) to removeoxide from areas other than the SON region. The thickness of the layerof oxide material will be substantially the same as the thickness of thegermanium containing layer 24. A hard mask 30′ is deposited on theresulting structure. A soft (for example, photoresist) mask (not shown)is deposited on the hard mask 30′ to facilitate selective removal of theportion of the hard mask 30′ on the pFET region of the structure. Astructure resulting from such mask deposition and partial removal isshown in FIG. 10. The deposition and selective removal of hard and softmasks is familiar to those of skill in the art.

Referring to FIG. 11, the structure obtained following the stepsdescribed above with respect to FIGS. 1-10 is thermally annealed. Theanneal process can be furnace anneal, rapid thermal anneal, flashanneal, or any suitable combination of those processes. The annealtemperature ranges from 600 degrees to 1300 degrees Centigrade. Theanneal time ranges from 1 millisecond to 2 hours, depending on theanneal temperature. Higher anneal temperatures require shorter annealtimes. A typical anneal condition is about 30 minutes at 1000° C. Suchannealing causes the mixing of the germanium containing layer 24 and thecrystalline silicon layer 26 in the pFET region of the structure. Asilicon germanium layer 38 is thereby formed on the carbon doped siliconlayer 22. The resulting silicon germanium layer 38 will have a germaniumcontent that is lower than that of the germanium containing layer 24.The germanium content of the silicon germanium layer 38 can beengineered as desired for particular applications by depositing agermanium containing layer 24 having an appropriate germanium contentand/or thickness for the particular applications.

The second applied hard mask 30′ is removed from the structure followingthe annealing process. Silicon germanium fins 40 are formed in the pFETregion of the structure from the silicon germanium layer 38. Siliconfins 42 are formed from the silicon layer 26 in the nFET region of thestructure 50. The pFET and nFET regions comprising the fins 40, 42 areelectrically isolated by the STI region as shown in FIG. 12. Techniquesfor forming finned structures for use in FinFET devices are known to theart and continue to be developed. Sidewall image transfer (SIT) is oneexemplary and conventional technique for defining fin thickness. US Pub.No. 2012/0068264, which is incorporated by reference herein, disclosesother techniques for forming narrow fins on semiconductor substratesthat can be applied to the structures disclosed herein. The carbon dopedsilicon layer 22 functions as an etch stop in the pFET region when thesilicon germanium layer 38 is processed to form the fins 40.

Technology for forming pFET and nFET devices on finned structures isknown and continues to be developed. The gates of FinFETs can be formedusing a “gate-first” process wherein a gate stack and spacers are formedprior to selective epitaxial growth on the fins wherein source and drainregions are enlarged. A “gate-last” process may alternatively beemployed. Gate-last procedures can involve making a dummy gate,fabricating other elements of the transistor, removing the dummy gate,and replacing the removed dummy gate with actual gate materials.

Doped semiconductor material such as silicon germanium (SiGe) may beprovided by selective epitaxial growth on the sidewalls of the finstructure(s) during fabrication of FinFET devices. Such growth resultsin faceted structures that, in some cases, merge into a continuousvolume.

If a gate-first process as described above is employed, gate materialsmay comprise a gate dielectric (e.g., high-k such as hafnium oxide) anda gate conductor (e.g., metal gate). Any suitable deposition techniquecan be used to deposit high-k and metal gate, including but not limitedto atomic layer deposition, chemical vapor deposition, physical vapordeposition, sputtering, plating, etc. Gate material can be formed bothabove and between the fins in some embodiments or, alternatively, onlybetween the fins. Dielectric spacers are formed around the gatestructure. If a gate-last process is employed, a dummy gate (not shown)is formed wherein the dummy gate may comprise a dummy gate dielectric(e.g., oxide) covering fins and a dummy gate material (e.g.,polysilicon) on top of the dummy gate dielectric. This dummy gate isremoved in a later process familiar to those of skill in the art and areplacement metal gate composition is patterned at an appropriate stageof the transistor fabrication process. Fin heights, widths and spacingare further chosen in accordance with manufacturer preferences. Finheights in some embodiments range between 10-50 nm. As discussed above,fin heights in the nFET region correspond to the thickness of thedeposited silicon layer 26 from which they are formed. The side walls ofthe crystalline silicon fins 42 and silicon germanium fins 40 are (110)surfaces in one or more embodiments. The side walls of the fins 40, 42may not be exactly vertical, and instead converge towards the tops ofthe fins. Surfaces described as (110) surfaces herein are at least closeto being (110) surfaces but may or may not be exactly (110) surfaces.

Once obtaining the structure as described above with respect to FIG. 12(or FIG. 13 as described below) and gate structures have been formedthereon, source/drain regions are formed on the fins by diffusion,implantation or other techniques familiar to those of skill in the art.In some embodiments, a layer (not shown) of doped material (for example,silicon germanium) may be grown epitaxially or otherwise deposited onthe structure, causing the source/drain regions to be merged in someembodiments or form diamond-shaped, unmerged structures in otherembodiments. In the fabrication of a pFET structure, boron-doped SiGecan be employed in one or more embodiments for the epitaxial growth ofvolumes (not shown) on the sidewalls of the silicon germanium fins 42.To fabricate nFET structures, volumes are formed with phosphorus-dopedsilicon (Si:P) in some embodiments. The doping can be chosen as desiredfor particular transistor applications. In one exemplary embodimentwhere the doped source/drain semiconductor material is SiGe, the dopantis boron in a concentration ranging 4-7e20 and the resulting FinFETstructure is p-type. Further fabrication steps are performed, some ofwhich depend on the particular FinFET structure to be obtained.Typically the grid comprising the parallel fins and gate structures arefilled with a low k dielectric material. Depending on the type of gateprocessing employed (gate-first or gate-last), appropriate steps arealso taken to complete gate fabrication.

Referring to FIG. 13, the areas between the silicon germanium fins 40are filled with a dielectric material such as an oxide (for examplesilicon dioxide (SiO₂)), forming isolation regions 44. Such material canbe deposited in accordance with conventional techniques such as highplasma density deposition. The thicknesses of the isolation regions 44above the carbon doped silicon layer can be engineered by oxide fill,then CMP (chemical mechanical planarization) to the top of the gatenitride cap (not shown), and then timed recess RIE (reactive ion etch)to approximate the thickness of the oxide layer 36 in the nFET region,in which case the heights of the silicon germanium fins 40 above theisolation regions 44 would be substantially the same as the heights ofthe silicon fins 42 in the nFET region.

Given the discussion thus far and with reference to the exemplaryembodiments discussed above and the drawings, it will be appreciatedthat, in general terms, an exemplary fabrication method includesobtaining a structure comprising a bulk silicon substrate, an epitaxiallayer comprising carbon doped silicon on the substrate, an epitaxiallayer containing germanium on the carbon doped silicon layer, and alayer comprising crystalline silicon on the germanium containing layer.Such as structure is illustrated in FIG. 4 and may be obtained byfabrication as described above or purchased at least in part from avendor. The method further includes forming an isolation region on thestructure electrically isolating a first region of the structure from asecond region of the structure. As shown in FIG. 5, a shallow trenchisolation region 28 is formed to electrically isolate first and secondregions of the structure later used to form pFET and nFET devices. Thegermanium containing layer is removed from the second region of thestructure, thereby forming a space within the second region beneath thecrystalline silicon layer. As discussed above, the second region islater used to form an nFET device. An insulating layer such as an oxidelayer 36 is formed within the space. The method further includesthermally mixing the germanium containing layer and the crystallinesilicon layer in the first region of the structure to form a layercomprising silicon germanium. A plurality of fins comprising silicongermanium are formed in the first region from the silicon germaniumlayer. Crystalline silicon fins are formed from the silicon layer in thesecond region. It will be appreciated that at least some of theabove-referenced steps may not necessarily be performed in the samesequence described above. As discussed above, the germanium containinglayer comprises silicon germanium in one or more embodiments.

A further exemplary fabrication method includes depositing an epitaxialcarbon doped silicon layer 22 on an essentially undoped siliconsubstrate 20, depositing an epitaxial silicon germanium layer on thecarbon doped silicon layer, and depositing an essentially undopedepitaxial silicon layer 26 on the silicon germanium layer, therebyforming a first structure, such as shown in FIG. 4, comprising thesilicon substrate, the carbon doped silicon layer, the silicon germaniumlayer and the epitaxial silicon layer. A shallow trench isolation region28 is formed within the first structure. The silicon germanium layer 24on a first side of the shallow trench isolation region is removed,thereby forming a space 34 within the first structure beneath theepitaxial silicon layer 26. The space is filled with an electricallyinsulating material as shown in FIG. 9. The method further includes thestep of thermally mixing the silicon germanium layer and the epitaxialsilicon layer on a second side of the shallow trench isolation region,thereby forming a silicon germanium surface layer 38. A first set ofparallel fins 42 is formed from the epitaxial silicon layer on the firstside of the shallow trench isolation region and a second set of parallelfins 40 is formed from the silicon germanium surface layer on the secondside of the shallow trench isolation region 28. FinFET devices (notshown) can be formed on the resulting structure.

A structure provided in accordance with the disclosure includes bulksilicon germanium fins for use in association with one or more pFETdevices and silicon on insulator fins used in nFET devices. Thestructure is in wafer form in one or more embodiments. An epitaxialcarbon doped silicon layer 22 is present on bulk silicon substrate 20.Fins 40 comprising silicon germanium adjoin a first portion of theepitaxial carbon doped silicon layer 22. An insulating layer 36 adjoinsa second portion of the epitaxial carbon doped silicon layer. Theinsulating layer is an oxide layer in one or more embodiments andadjoins the top surface of the Si:C layer. A plurality of fins 42comprising crystalline silicon adjoin the insulating layer. An isolationregion 28 electrically isolates the first and second portions of theepitaxial carbon doped silicon layer 22. Such an exemplary structure isshown schematically in FIG. 12. In some embodiments, the structurefurther includes an isolation layer 44 extending between the silicongermanium fins 40 as shown in FIG. 13.

Those skilled in the art will appreciate that the exemplary structuresdiscussed above can be distributed in raw form or incorporated as partsof intermediate products or end products that benefit from having FinFETdevices therein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof Terms such as “above” and “below” are used to indicate relativepositioning of elements or structures to each other as opposed torelative elevation.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the various embodiments has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the forms disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope and spirit of the invention. The embodiments were chosen anddescribed in order to best explain the principles of the invention andthe practical application, and to enable others of ordinary skill in theart to understand the various embodiments with various modifications asare suited to the particular use contemplated.

What is claimed is:
 1. A method comprising: obtaining a structurecomprising a bulk silicon substrate, an epitaxial layer comprisingcarbon doped silicon on the substrate, an epitaxial layer containinggermanium on the carbon doped silicon layer, and a layer comprisingcrystalline silicon on the epitaxial layer containing germanium; formingan isolation region on the structure electrically isolating a firstregion of the structure from a second region of the structure; removingthe epitaxial layer containing germanium from the second region of thestructure, thereby forming a space within the second region beneath thelayer comprising crystalline silicon; forming an insulating layer withinthe space; thermally mixing the epitaxial layer containing germanium andthe layer comprising crystalline silicon in the first region of thestructure to form a layer comprising silicon germanium; forming aplurality of fins comprising silicon germanium in the first region fromthe silicon germanium layer, and forming a second plurality of fins fromthe layer comprising crystalline silicon in the second region.
 2. Themethod of claim 1, wherein the layer comprising crystalline silicon hasa thickness of fifty nanometers or less.
 3. The method of claim 2,wherein the epitaxial layer containing germanium comprises silicongermanium.
 4. The method of claim 3, wherein the step of forming theinsulating layer within the space includes filling the space with anoxide material.
 5. The method of claim 3, wherein the epitaxial layercontaining germanium comprises 20-80% germanium.
 6. The method of claim5, wherein the epitaxial layer containing germanium has a thicknessbetween five and twenty nanometers.
 7. The method of claim 1, furtherincluding the step of forming gate structures on the structure.
 8. Themethod of claim 1, further including the step of forming a p-type FinFETdevice in the first region using the silicon germanium fins.
 9. Themethod of claim 8, further including the step of forming a n-type FinFETdevice in the second region using the fins formed from the layercomprising crystalline silicon.
 10. The method of claim 9, wherein thestep of removing the epitaxial layer containing germanium from thesecond region of the structure includes forming a trench through thelayer comprising crystalline silicon and etching the epitaxial layercontaining germanium.